MONTPELIER — Schools are closed across southern Vermont and a winter storm warning is in effect for Vermont’s four southernmost counties with 6 to 12 inches of snow possible.The National Weather Service says some snow was going to fall early Thursday, but the storm is not scheduled to begin in earnest until later in the day. And it’s going to be cold.The forecast for southern Vermont calls for a high of 9 on Thursday, an overnight low of -eight and on Friday a high of zero.It’s part of a storm system that is expected to dump similar amounts of snow across much of southern New England and parts of New York.The winter storm watch remains in effect until 10 a.m. Friday.